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. 2019 Jun 18;21(6):e13475. doi: 10.2196/13475

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©Ke Yun, Junjie Xu, Sequoia Leuba, Yunyu Zhu, Jing Zhang, Zhenxing Chu, Wenqing Geng, Yongjun Jiang, Hong Shang. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 18.06.2019.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on http://www.jmir.org/, as well as this copyright and license information must be included.

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Flowchart of study selection criteria from a prospective cohort of men who have sex with men from 2009 to 2016 in Shenyang, China.